Broadband Communication Systems (BCSs), often referred to simply as cable systems, have been installed in many communities throughout the United States and elsewhere worldwide in recent years. The bandwidth available on such systems allows many sources of entertainment programming and information to be made available to large populations of people with few effects of interference and other problems often associated with over-the-air broadcasting. The BCS infrastructure is also available for returning signals from the installation site to a central location, so-called upstream signaling, for purposes such as internet access and telecommunications using voice over internet protocols (VoIP) and the like, including establishment of virtual private networks (VPNs).
BCSs operate over frequency bands which overlap with over-the-air/broadcast frequency bands, some of which serve important commercial and safety purposes such as aviation communications. Interference with such broadcast communications is, in theory and substantially in practice, avoided by confining the BCS signals within shielded cables. Therefore, BCS operators expend extraordinary efforts to maintain BCS systems to avoid signal egress and to detect and rapidly repair any shielding flaw or signal egress that may occur. Numerous sophisticated systems have been developed for such purposes as well as improving the efficiency with which such purposes may be accomplished.
A symmetrical effect to signal egress is signal ingress in which an ambient electromagnetic signal enters into the BCS cable through a shielding flaw or deficiency. The signal distribution portion of a BCS is usually designed and installed with great care to provide a highly robust system which is, nevertheless, subject to damage and degradation from ambient conditions such as weather. Since signal egress can be more-or-less easily detected and repairs performed, those repairs are effective to remedy sources of signal ingress into the distribution portion of the BCS, as well.
It has been the practice to use optical communications through optical fiber cable over ever larger portions of the BCS since optical communication media are generally less subject to damage and signal attenuation over their geographical extent and damaged portions of such fiber optic cables do not result in electromagnetic field signal egress or ingress. Nevertheless, shielded cable remains the medium of choice for terminal portions of the BCS and for connection of subscriber equipment such as modems and so-called set-top boxes to interface to subscriber equipment such as televisions, computers and other communication equipment.
While expenditures for good design of the signal distribution portion of a BCS are economically effective, the same is not true for subscriber installations. Rather, hardware such as cable, connectors, directional couplers, signal splitters, amplifiers and the like have been carefully designed and largely standardized such that adequate shielding within a subscriber site will generally be provided by their routine use and assembly at the subscriber site. Nevertheless, the BCS operator has no control over or even knowledge of other devices that may be present at a subscriber site that may be sources of potentially large electromagnetic signals within the bands of frequencies at which the BCS operates. Many potential sources of such noise such as electric motors in heating/cooling systems, refrigerators, dishwashers, fans and the like or even electric lighting and entertainment devices that are seldom thought of as radio frequency (RF) noise sources may be present and radiate substantial RF noise. Further, inadequate assembly by the subscriber of well-designed components that may be as simple as inadequate tightening of a connector or the use of readily available and inexpensive but low quality components may function as a shielding flaw allowing ambient RF noise or broadcast signal ingress into the BCS. Moreover such noise can accumulate for a plurality of subscriber installations along the BCS system and be summed by the BCS system itself until it may reach a level which compromises upstream signaling. Therefore, it is important to assure shielding integrity at the subscriber site. Unfortunately, arrangements for quantitatively measuring signal ingress at a subscriber site have only been capable of measuring noise levels above the intended signal levels on the BCS or have required additional expensive and cumbersome equipment for indirectly measuring effectiveness of shielding.